07/20/2014 10:55 EDT | Updated 09/19/2014 05:59 EDT

The Long-Term Trauma of Gastrointestinal Infection

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Most of us have experienced at one time or another that rumble in the gastrointestinal jungle. The symptoms are well-known: gas, pain, diarrhea and an overall wish to hide until the scourge subsides. Most gut infections are short-lived and tend to resolve on their own allowing us to continue our normal lives. But there is a darker side to these maladies manifesting at the microbial level. Though we may not feel these consequences in the short term, research has shown there may be more difficult times down the road.

The first investigations into the long term effects of an intestinal infection were conducted back in the 1960s. Using mice as a model, a pathogenic form of E. coli was tested to observe the progress of war. Several observations were made which at the time were considered to be interesting. When first introduced, the bacteria would attack the natural microbiota. If the mouse was sufficiently resistant, there was no infection. Yet, if the villain overcame the defence, the mouse would suffer. But there was another shocking result. Even after infection passed, some the good bacteria including lactose fermenting probiotic bacteria such as the lactobacilli, never returned.

The results were investigated more closely over the years but never made the leap to the human condition. That changed 40 years later with a rise in cases of the now infamous Clostridium difficile. As cases were rising exponentially at the time, researchers wanted to find out whether changes in the gut were involved. Sure enough, they found those who were suffering from clinical disease had an entirely different microbial profile than healthy individuals with significantly less good bacteria. C. difficile had somehow managed to cause trauma in the gut sending the good bacteria away. Even more intriguing was the association between age and infection with the elderly taking the short end of the stick. The key to this difference was the involvement of the immune system and the involvement of another well-known cause of disease: chronic inflammation.

By 2012, this process of invade, injure and inflame had been attributed to a number of different pathogens. Unfortunately, there was little that could be done to either halt or remedy the situation. There was little data to show exactly what happened after a short term infection subsides. To better understand how to treat, there needed to be more of these longer studies.

Last week, an American group of researchers took us one step further in that direction. They reported on their attempts to understand the dynamics of the gut microbial population before, during and after and infection. Their goal was to develop a list of microbial 'signatures' to better understand the progression of change in the body so that treatments could at least be followed. They also aimed to better understand how a battle could affect the entire gut landscape and whether the resultant post-traumatic stress was local or universal.

To do this, they used a mouse model known to have gastrointestinal infections -- acute and chronic -- similar to humans. The team infected the mice and then over time identified the residents of the microbiota in all areas of the intestines. Much like rural areas, the ileum and cecum saw both rises and falls in population depending on the course of infection. When times were bad, the population dispersed but for the most part returned to normal after the infection ended. The colon, however, was like a destroyed urban centre in which infection led to a massive exodus of bacteria that never fully recovered. The damage left the environment inhospitable to most with only certain opportunists -- such as C. difficile -- ready to re-colonize and cause even more trouble.

The results offered insight into how the colon appears to suffer the greatest during an infection as well as why chronic diseases of the colon can occur. The loss and lack of restitution of good bacteria -- dysbiosis -- could leave the environment ripe for other pathogens to enter and cause problems. Even worse, the absence could lead the body to believe it may be in a cold war, requiring chronic inflammation as a precaution. Over time, this could inevitably lead to other problems such as gastrointestinal disorders.

Though the picture may appear gloomy for anyone who might have a gastrointestinal infection there is some hope. Ingestion of probiotics may help to recolonize the colon. Adding a good diet rich in prebiotics and fibre will help the bacteria re-establish their home and invite other friendly bacteria to come back. Though it may take some time, the effort is worthwhile. After all, nobody deserves to deal with the long lasting stresses of trauma, not even your microbes.


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